The present invention addresses a need in the art to reliably and safely increase throughput of large format ink jet print engines. One constraint impeding the ability to increase printing speed (typically expressed as a square foot/hour measurement) of large format ink jet print engines is ink drying characteristics and the amount of ink expelled upon the media (or "ink coverage" typically expressed as a percentage of coverage by a given color of ink). The physical make up of the printing surface, any coatings present on the printing substrate, the type of ink applied, and whether any post-printing drying or vapor recovery treatment(s) are applied all contribute to a reliable and safe rate of throughput for large format print engines.
Ambient conditions affect the ability to print high quality prints at an efficient rate of throughput. In fact, a rise of relative humidity (RH) of just a few percent can inhibit ink drying in at least two ways. First, if the printing media is not insulated from the rising humidity, the media itself can acquire a moisture content that will in effect displace the ink that is later applied, with the result that the media simply cannot absorb as much ink as when it is "dry." Second, if the ambient atmospheric conditions become saturated, the ability of the ink to dry (or be absorbed into the ambient air) is inhibited and thus, printed output will dry only slowly. Particularly with roll-based media printed in quantity (or banner prints), if printed media is not fully dry after printing the print might transfer to the back of an adjacent portion of media, or smudge, when the printing substrate is rolled prior to cutting into individual images.
In the prior art, a variety of forced air dryers have been employed to increase the evaporation and drying of ink printed onto a section of media. In addition, some prior art approaches link one or more atmospheric sensors to a printing control unit to slow printing operations when ambient conditions do not promote drying. Also, some prior art techniques have used a "media loop" (in conjunction with a proximity sensor disposed to sense the presence of said media loop) wherein the just-printed media passively hangs prior to being rolled to thereby increase the drying time, or exposure of the media to ambient drying conditions.
When the type of inks used contain agents to promote drying, or when the ink itself releases vapors and possibly harmful air-borne material, a dedicated system for removing said vapors or possibly harmful air-borne material has been implemented in large-scale printing systems--but to the inventors' knowledge no such system has even been combined into a single unit, nor adapted to operate in conjunction with a single large format thermal ink jet print engine.
The present invention thus finds utility over a variety of printing platforms that operate to simply expel air in the vicinity of printed output and also offers vapor recovery/evacuation from a common assembly so that thermal ink jet printing can be successfully practiced over a large variety of atmospheric conditions and in conjunction with a large variety of solvent-based inks compositions.